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Millett "Starving Student" hybrid amp

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  1. Logos
    Thanks again, Tom! Here are some pics for your enjoyment:

    Ocean Green!
    [​IMG]

    Spot the Gamma 1
    [​IMG]

    Headphone Love
    [​IMG]

    Thanks for looking! [​IMG]

    P.S. Kitarist: Do it!
     
  2. simwells
    Finally got my tubes this morning and it does sound really good, letting it burn it atm.

    Here's my little P2P version;

    [​IMG]
     
  3. UKToecutter
    Thats a very nice looking and compact build...
     
  4. the_equalizer
    Quote:

    Originally Posted by Logos /img/forum/go_quote.gif
    Thanks again, Tom! Here are some pics for your enjoyment:

    <snip>

    Thanks for looking! [​IMG]

    P.S. Kitarist: Do it!




    Nice pics! I like the Grado's + SSMH combo a lot.

    Quote:

    Originally Posted by simwells /img/forum/go_quote.gif
    Finally got my tubes this morning and it does sound really good, letting it burn it atm.

    Here's my little P2P version;





    Cool build! You even managed to find a couple 19J6 tubes, congratulations!

    cheers!
     
  5. simwells
    Quote:

    Originally Posted by the_equalizer /img/forum/go_quote.gif
    Cool build! You even managed to find a couple 19J6 tubes, congratulations!

    cheers!




    I may (debating what to do with them) have a couple spare too.
     
  6. UKToecutter
    Quote:

    Originally Posted by simwells /img/forum/go_quote.gif
    I may (debating what to do with them) have a couple spare too.



    I'd keep a hold of them if I were you.

    You never know how long the ones you're using will last !!!!
     
  7. Jrome
    So I finally got my replacement tube! (Thanks TomB!)


    Everything works and it sounds awesome. One quick question, the tube on the right is glows slightly brighter than the one on the left. Is this a cause for concern?
     
  8. tomb
    Quote:

    Originally Posted by Jrome /img/forum/go_quote.gif
    So I finally got my replacement tube! (Thanks TomB!)


    Everything works and it sounds awesome. One quick question, the tube on the right is glows slightly brighter than the one on the left. Is this a cause for concern?




    No - no cause for concern. Every tube glows somewhat differently. Even if you switched them and noticed that the right side still glow brighter, the circuit itself splits the voltage through resistors. That usually results in one side being slightly brighter than the other s imply because of the minute differences in resistors.
     
  9. ethan961
    A few months ago I had a problem, it seemed that there was a short and one tube was getting 48v. Well, after months of off and on searching for the short, I discovered that one of the FEts had gone bad and was providing no resistance. Replaced that and everything is working great [​IMG] I'm not sure if this has been posted before but that's just my experience.
     
  10. Entropy1
    So I just swapped out the MOSFETs (thanks a lot tomb) and am getting the channel bleed. Before the MOSFET swap, it wouldn't even turn on, but that also means I might be in a position to kill this set too. I don't know what is going on. Between the metal on the MOSFETs and ground there is ~4k which I'm hoping is okay as i spent a bit of time making sure they were isolated. It seems to me as if there must still be two issues as the still present significant volume difference and channel bleed are still both present. I've gone over all the soldering and wiring connections several times and have failed to spot a problem. Does anyone have any ideas or what would be some good resistances to check? Thanks for any help.
     
  11. Entropy1
    I've been checking resistances and for some reason decided to check the resistance directly from the input to the output expecting to get no continuity from each channel. For some reason though, I am getting just over 100k between the left input and left output, right output and ground. The right channel yields infinite resistance between everything as i believe it should. Any ideas on how this could have happened? I don't see any solder bridges and am pretty puzzled by it. Thanks again.

    Edit: there appears to be some resistance between left and ground at the terminal block input. This also exists with the wires connecting the rca jack disconnected.
     
  12. the_equalizer
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    I've been checking resistances and for some reason decided to check the resistance directly from the input to the output expecting to get no continuity from each channel. For some reason though, I am getting just over 100k between the left input and left output, right output and ground. The right channel yields infinite resistance between everything as i believe it should. Any ideas on how this could have happened? I don't see any solder bridges and am pretty puzzled by it. Thanks again.

    Edit: there appears to be some resistance between left and ground at the terminal block input. This also exists with the wires connecting the rca jack disconnected.




    Resistance measurements in circuit do not usually say much. If you look at the schematic, you can see that at the input terminal block, you can expect to see a resistance of 50K (the volume pot) from the live wire to ground.

    Measuring MOSFET isolation could turn out to be somewhat tricky too, but 4K definitely does not seem right; the value should be up in the megohm range. The MOSFET's metal tab is electrically connected to pin 2, if I remember correctly. If you look at the schematic you can see that there's a big decoupling capacitor (C1) strapped from both the MOSFETs' pin 2 to ground, which will affect the measurement.

    Connected between the 48 volt line (which is connected to the MOSFETs' pin 2) and ground you also have the series combination or R13 and the parrallel combination of R2-R4 and R8-R10 which totals 222Kohms; again affecting your measurements of MOSFET tab to case isolation.

    cheers!
     
  13. Entropy1
    Thanks for the response. I'm aware that the readings don't necessarily mean much but I'm hoping that the discrepancies at the same points of each channel should tell me if any inconsistencies that might exist. Are there any better approaches I should be taking? Thanks again.
     
  14. the_equalizer
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    Thanks for the response. I'm aware that the readings don't necessarily mean much but I'm hoping that the discrepancies at the same points of each channel should tell me if any inconsistencies that might exist. Are there any better approaches I should be taking? Thanks again.



    Well, in the case of measuring the MOSFET to case isolation, and if this is a PCB beezar.com build we're talking about, I'd make sure the sliding aluminum panel to which the MOSFET's are bolted is not grounded when I take the measurement, so that the capacitor and resistors I mentioned before do not influence the measurement.

    To this end I would completely remove the panel from the case and I'd temporarily remove the standoff, then I'd measure the resistance from MOSFET tab to aluminum panel, which should be in the megohm range.

    As to the other circuit problems, it's difficult to imagine what could be causing the channel bleed. The volume difference could be caused by cold solder joints, bad MOSFETs, wrong value resistors, defective volume pot, etc, etc, Maybe you could provide us with some clear pictures of your wiring and of the PCB ?

    cheers!
     
  15. tomb
    Quote:

    Originally Posted by Entropy1 /img/forum/go_quote.gif
    Thanks for the response. I'm aware that the readings don't necessarily mean much but I'm hoping that the discrepancies at the same points of each channel should tell me if any inconsistencies that might exist. Are there any better approaches I should be taking? Thanks again.



    Pics?
     
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